Milky Way as a kiloparsec-scale axionscope
Milky Way as a kiloparsec-scale axionscope
Very high energy gamma rays are expected to be absorbed by the extragalactic background light over cosmological distances via the process of electron-positron pair production. Recent observations of cosmologically distant gamma-ray emitters by ground based gamma-ray telescopes have, however, revealed a surprising degree of transparency of the universe to very …